Printing has been conventionally performed using ink, toner, and other colorants. Some printing processes include color conversion for converting image data from its original color space (the RGB color space, for example) to the color space of the colorant used in printing (the CMYK color space, for example). Here, a technique was proposed for suppressing a reduction in the color gamut for low-lightness regions while limiting the total magnitude of color signals corresponding to the colorants used for printing (reducing the values of the color signals in order to reduce the amount of colorant used) by adjusting the color signal for black in addition to the color signals for cyan, magenta, and yellow.